1. Field of the Invention
The present invention relates to an electronic device whose electrodes and wiring are constructed by aluminum or a material containing aluminum as the principal component. It also relates to a method for manufacturing the same.
2. Description of the Related Art
Recently, active-matrix liquid crystal devices equipped with large-area image planes are attracting much attention. Such active-matrix liquid crystal devices not only require image planes having larger area, but also demand for finer patterning.
The use of a material having low electric resistance for the wiring material is necessary to fulfill the demand above, because the delay of signal propagating on wiring becomes a problem in a device with a size of 10.times.10 inch.sup.2 or larger.
Concerning a wiring material having low electric resistance, aluminum is the most desirable one. However, aluminum brings about the problem of heat resistance on its use in the manufacturing method (refer to a review paper in Display and Imaging, 4 (1996), pp. 199-206; published by Science Communications International).
More specifically, in the steps such as the formation of various types of thin films by deposition and the annealing of the resulting films, or in the irradiation of laser light and the implantation of impurity ions, aluminum undergoes problematic abnormal growth so as to form protrusions called hillock or whisker. These hillock and whisker are believed to be attributable to the poor heat resistance of aluminum.
Those protrusions known as hillock or whisker sometimes grow as long as 1 .mu.m or even longer. This phenomenon leads to the occurrence of short circuit between wirings.
The problem above can be prevented from occurring by forming an anodic oxide film on the surface of the aluminum wiring (see the reference above).
According to the study of the present inventors, it is found that the anodic oxide film (assumably containing Al.sub.2 O.sub.3 as the principal component) is robust and is effective for preventing hillock or whisker from generating. On the other hand, however, such a robust material makes it difficult to form contact holes on the aluminum wiring.